The present invention relates generally to the determination of the surface areas of fasteners, and in particular relates to a method and apparatus for determining the surface area of a threaded fastener.
The desire to determine the corrosion rate of a fastener is founded in any given number of applications. For instance, in most timber engineering applications, wood is in intimate contact with metallic fasteners that are embedded in the wood. The last half of the 20th century has seen an increase in the use of threaded fasteners, such as wood screws, deck screws, drywall screws, annularly threaded nails, and the like. It is well known that such fasteners are subject to corrosion due to the presence of water and oxygen in the cellular structure of wood. Conventionally, the waterborne preservative CCA (chromated copper arsenate) had been used to extend the service life of outdoor wood structures. Due to the voluntary withdrawal of CCA for residential use, many designers are now choosing to use alternatives such as ACQ (alkaline copper quaternary) and CuAz (alkaline copper azole). However, limited knowledge has been attained regarding the effects of alkaline based preservatives on the corrosion of fasteners in contact with wood.
While standard exposure tests as well as accelerated tests are known for the evaluation of corrosion of a fastener in ACQ-treated wood, the accuracy of these tests is dependent on the ability to precisely measure the various quantities used to calculate the corrosion rate. In a weight loss test, for instance, the calculation depends on the duration of the test, the mass of the fastener, and the surface area of the fastener. It has been found during corrosion testing that as the duration of the test is increased, the uncertainty in the corrosion rate measurement is increasingly dominated by uncertainties in the measurement of the surface area of the fastener.
Electrochemical corrosion tests are also being developed for fasteners in treated wood. Such tests can have lower experimental variation, thus rendering accurate calculation of surface area even more important.
Accordingly, what is needed is a method and apparatus for determining the surface area of a fastener, such as a threaded fastener. It would be further desirable that the method and apparatus for determining the surface area of a threaded fastener be versatile and applicable to determining the surface are of other fastener types, such as non-threaded fasteners.